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<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <script src="./call.js"></script>
</head>
<body>
  <script>
    // 声明一个函数
    function add(a, b) {
      console.log(this);
      return a + b + this.c;
    }

    // 声明一个对象
    let obj = {
      c: 521
    }

    // 添加全局属性
    var c = 1314;

    // 执行call
    console.log(call(add, obj, 9, 8)); //538
    console.log(call(add, null, 9, 8)); //1331
    console.log(obj);
  </script>
</body>
</html>